1. Field of the Invention
This invention relates to slide fasteners and to a method for making the same, and in particular to the structural formation of the filamentary coils for slide fasteners.
2. Description of the Prior Art
It has been conventional for the coil of slide fasteners to be formed from filamentary material with each convolution of the coil having head and heel elements interconnected by leg elements; simultaneous formation of a pair of coils has been accomplished on coiling machines which shape the convolutions of the filamentary coils on suitable mandrels and intermesh such coils after their formation.
U.S. Pat. Nos. 1,937,297, 2,296,880, 2,300,442, 2,300,443, 2,541,728, 2,643,432, 2,907,066, 2,973,554, 3,053,288, 3,145,523, 3,152,433, 3,196,489, 3,553,782 and 3,609,827 are representative of the prior art in illustrating a variety of cross sections for the interlocking elements of slide fasteners as well as a variety of methods and apparatuses for forming the same.
One of the problems associated with the prior art devices is that the manufacture of slide fastener coils having non-circular cross sections has resulted in slide fasteners that have a low index of flexibility and a high index of rigidity. While the prior art devices may have been satisfactory for the particular purpose for which they were designed, they have not been satisfactory in maintaining the proper flexibility for the different types and sizes of slide fasteners utilizing filamentary coil of the plastic type. The many methods and apparatus in the prior art have served their particular purposes with respect to the types of slide fastener coils for which they were designed. However, such prior art arrangements have always utilized a symmetrical association of coiling steps and mandrel configuration.